An organic electroluminescence device is a device that includes a thin film made of a fluorescent organic compound between an anode and a cathode, generates an exciton from the fluorescent compound by injection of an electron and an electron hole (hereinafter, also simply referred to as a hole) from each electrode, and uses light to be radiated when the exciton returns to the ground state.
The study conducted by Eastman Kodak Company in 1987 (Appl. Phys. Lett., 51, p. 913, (1987)) reported light emission at about 1,000 cd/m2 by an applied voltage of about 10 V from a device including a function-separated two-layer structure having an anode made of ITO and a cathode made of magnesium-silver alloy where an aluminum quinolinol complex is used as each of an electron-transporting material and a light-emitting material and a triphenylamine derivative is used as a hole-transporting material. In this case, related patent documents include U.S. Pat. Nos. 4,539,507, 4,720,432, and 4,885,211.
In addition, light emission at spectra ranging from ultraviolet through infrared is possible by changing the type of a fluorescent organic material. Recently, various compounds have been studied actively and described in many publications such as U.S. Pat. Nos. 5,151,629, 5,409,783, and 5,382,477, Japanese Patent Application Laid-Open Nos. H02-247278, H03-255190, H05-202356, H09-202878, and H09-2275756.
Furthermore, in addition to the organic electroluminescence devices using low molecular weight materials as described above, an organic electroluminescence device using a conjugated polymer has been reported from the group of Cambridge University (Nature, 347, 539 (1990)). This report has confirmed light emission from a monolayer by film formation with polyphenylene vinylene (PPV) in a coating system. Patents related to an organic electroluminescence device using a conjugated polymer include U.S. Pat. Nos. 5,247,190, 5,514,878, and 5,672,678, Japanese Patent Application Laid-Open Nos. H04-145192, and H05-247460.
Recently, furthermore, an organic phosphorescence device using an iridium complex such as Ir (ppy)3 (Appl. Phys. Lett., 75, 4 (1999)) has been attracting attention and high luminous efficiency thereof has been reported.
Recent advances in organic electroluminescence devices are remarkable and the characteristics thereof allow the formation of light-emitting devices having high luminance with a low applied voltage, the variety of emission wavelengths, high-speed responsiveness, low profile, and lightweight, suggesting the possibility for extensive uses. However, organic electroluminescence devices still involve many problems in durability, such as chronological changes by prolonged use, and degradation with atmospheric gases containing oxygen, humidity, or the like. When applications of organic electroluminescence devices to full-color displays and so on are taken into consideration, under the present circumstances, blue-, green-, and red light-emissions with extended-life, high conversion rate, and high color purity have been demanded.
Examples of the materials and organic electroluminescence devices containing anthracene rings include a phenyl anthracene derivative disclosed in Japanese Patent Application Laid-Open No. H08-012600. In particular, when a phenyl anthracene derivative was used as a blue light-emitting material or an electron-injection transporting material, the phenyl anthracene derivative supposedly allows the formation of a good organic film because of its low crystallinity. However, the luminous efficiency and durable life of the phenyl anthracene ring were insufficient in practical application.
An aminoanthracene derivative and a diaminoanthracene derivative have been disclosed as other examples in Japanese Patent Application Laid-Open Nos. H09-157643 and H10-072579, respectively. In the documents, those materials supposedly generate green light-emission when they were used as light-emitting materials. However, devices prepared from those materials showed insufficient luminous efficiencies, and their durable lives were still insufficient in practical application.
Japanese Patent No. 3008897 discloses as another example a device using a particular bianthryl compound as a light-emitting material, which supposedly generates light emission with high luminance. However, the patent describes nothing about luminous efficiency and durable life.
Japanese Patent Application Laid-Open No. H11-008068 discloses as still another example a device using a particular anthracene compound having an olefin site as a light-emitting material, which supposedly generates light emission from yellow to red. However, the device showed insufficient luminous efficiency in practical application.
Furthermore, Japanese Patent Application Laid-Open No. 2001-284050 discloses as another example a device that contains an anthracene derivative having a particular structure, an electron-transporting compound, and another fluorescent compound in a light-emitting medium layer. This device supposedly provides a red light-emitting device with improved reliability. However, the device showed insufficient luminous efficiency in practical application. In addition, it was difficult to obtain blue light emission because of its device configuration.